Exposure mask substrate manufacturing method, exposure mask manufacturing method, and semiconductor device manufacturing method

ABSTRACT

A method of manufacturing an exposure mask substrate including a substrate and a light-shielding film formed on the substrate, comprising measuring a flatness of at least one substrate before formation of a light-shielding film, predicting, on the basis of a measurement result, the flatness of the substrate when the substrate is chucked on an exposure apparatus, selecting the substrate having a predetermined flatness on the basis of a prediction result, predicting, for the selected substrate, a desired flatness of the substrate after light-shielding film formation after a light-shielding film is formed on the substrate, forming a light-shielding film on the selected substrate, measuring the flatness of the substrate having the formed light-shielding film, and determining whether the substrate having the light-shielding film has the desired flatness after light-shielding film formation by comparing a measurement result with a prediction result of the flatness after light-shielding film formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom prior Japanese Patent Application No. 2003-155936, filed May 30,2003, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to an exposure mask substratemanufacturing method, an exposure mask manufacturing method, and asemiconductor device manufacturing method.

[0004] 2. Description of the Related Art

[0005] In recent years, problems in photolithography in thesemiconductor manufacturing process have become noticeable. Along withthe progress in size reduction of semiconductor devices, the need formicropatterning in photolithography has grown. The device design rulehas already been reduced to 0.1 μm, and the pattern size to becontrolled is 10 nm or less. That is, the accuracy required is verystrict.

[0006] Under these circumstances, the problem of flatness of photomasksused in photolithography has risen as a factor that impedes highyaccurate pattern formation. As the focus margin in photolithographydecreases along with size reduction of devices, the flatness of aphotomask has become non-negligible.

[0007] When the shape of a photomask chucked in an exposure apparatus ispredicted by simulation, the flatness of the photomask can be managed inactual use. Hence, the number of problems caused by the flatness ofphotomasks is becoming smaller than before where the flatness is notpredicted.

[0008] However, there is still a problem that a photomask shapepredicted by simulation does not coincide with the shape of a photomaskactually chucked in an exposure apparatus. This is because alight-shielding film formed on the photomask has internal stress. In aphotomask having a pattern with a large opening ratio, stress reliefcaused by removing the light-shielding film by etching changes theflatness of the mask.

BRIEF SUMMARY OF THE INVENTION

[0009] According to an aspect of the invention, there is provided amethod of manufacturing an exposure mask substrate including a substrateand a light-shielding film formed on the substrate, comprising:measuring a flatness of at least one substrate before formation of alight-shielding film; predicting, on the basis of a measurement result,the flatness of the substrate when the substrate is chucked on anexposure apparatus; selecting the substrate having a predeterminedflatness on the basis of a prediction result; predicting, for theselected substrate, a desired flatness of the substrate afterlight-shielding film formation after a light-shielding film is formed onthe substrate; forming a light-shielding film on the selected substrate;measuring the flatness of the substrate having the formedlight-shielding film; and determining whether the substrate having thelight-shielding film has the desired flatness after light-shielding filmformation by comparing a measurement result with a prediction result ofthe flatness after light-shielding film formation.

[0010] According to another aspect of the invention, there is provided amethod of manufacturing an exposure mask substrate including a substrateand a light-shielding film formed on the substrate, comprising:measuring a flatness of at least one substrate before formation of alight-shielding film; predicting, on the basis of a measurement result,the flatness of the substrate when the substrate is chucked on anexposure apparatus; selecting the substrate having a predetermined firstflatness on the basis of a prediction result; forming a light-shieldingfilm on the selected substrate; measuring the flatness of the substrateafter light-shielding film formation, the substrate having the formedlight-shielding film; predicting, on the basis of a measurement result,the flatness of the substrate when the substrate after formation of thelight-shielding film is chucked on the exposure apparatus; and selectingthe substrate having a predetermined second flatness on the basis of aprediction result.

[0011] According to another aspect of the invention, there is providedan exposure mask manufacturing method of manufacturing an exposure maskby using an exposure mask substrate including a substrate and alight-shielding film formed on the substrate, comprising: measuring aflatness of at least one substrate before formation of a light-shieldingfilm; predicting, on the basis of a measurement result, the flatness ofthe substrate when the substrate is chucked on an exposure apparatus;selecting the substrate having a predetermined flatness on the basis ofa prediction result; predicting, for the selected substrate, a desiredflatness of the substrate after light-shielding film formation after alight-shielding film is formed on the substrate; forming alight-shielding film on the selected substrate; measuring the flatnessof the substrate having the formed light-shielding film; andmanufacturing an exposure mask by forming a desired pattern on thesubstrate when it is determined by comparing a measurement result with aprediction result of the flatness after light-shielding film formationthat the substrate having the light-shielding film has the desiredflatness after light-shielding film formation.

[0012] According to another aspect of the invention, there is providedan exposure mask manufacturing method of manufacturing an exposure maskby using an exposure mask substrate including a substrate and alight-shielding film formed on the substrate, comprising: measuring aflatness of at least one substrate before formation of a light-shieldingfilm; predicting, on the basis of a measurement result, the flatness ofthe substrate when the substrate is chucked on an exposure apparatus;selecting the substrate having a predetermined first flatness on thebasis of a prediction result; forming a light-shielding film on theselected substrate; measuring the flatness of the substrate afterlight-shielding film formation, the substrate having the formedlight-shielding film; predicting, on the basis of a measurement result,the flatness of the substrate when the substrate after formation of thelight-shielding film is chucked on the exposure apparatus; selecting thesubstrate having a predetermined second flatness on the basis of aprediction result; and manufacturing an exposure mask by forming adesired pattern on the selected substrate.

[0013] According to another aspect of the invention, there is provided asemiconductor device manufacturing method comprising: chucking anexposure mask manufactured by the exposure mask manufacturing method inan exposure apparatus; and illuminating a pattern formed on the exposuremask, which is to be used to form a semiconductor element, by anillumination optical system to transfer an image of the pattern onto apredetermined substrate.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0014]FIG. 1 is a flowchart showing an exposure mask substratemanufacturing step according to the first embodiment of the presentinvention;

[0015]FIG. 2 is a flowchart showing an exposure mask substratemanufacturing step according to the second embodiment of the presentinvention;

[0016]FIG. 3 is a flowchart showing an exposure mask substratemanufacturing step according to the third embodiment of the presentinvention; and

[0017]FIG. 4 is a flowchart showing an exposure mask substratemanufacturing step according to the fourth embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] The embodiments of the present invention will be described belowwith reference to the accompanying drawing.

[0019] The outline of the first embodiment includes a first measurementstep of measuring the major surface flatness of a quartz substratebefore formation of a light-shielding film including a Cr film and ahalftone (HT) film, a step of simulating the major surface flatnessafter formation of the light-shielding film, which makes it possible toobtain a desired major surface flatness when a substrate prepared byforming the light-shielding film on the quartz substrate is chucked onthe mask stage of an exposure apparatus, a second measurement step ofmeasuring the major surface flatness of the substrate after thelight-shielding film is actually formed on the quartz substrate, and astep of comparing the result in the second measurement step with thesimulation result to determine whether the desired flatness can beobtained.

[0020]FIG. 1 is a flowchart showing an exposure mask substrate (maskblank) manufacturing step according to the first embodiment of thepresent invention. The exposure mask substrate manufacturing stepaccording to the first embodiment will be described below with referenceto FIG. 1 and Tables 1 and 2 (described later).

[0021] Table 1 shows the results of flatness measurement and predictionof 10 quartz substrates (glass substrates) (A to J). Each quartzsubstrate is 6 inches square (152 mm square) and has a thickness ofabout 6 mm. TABLE 1 Flatness of Quartz Substrate (μm) Flatness MaskMajor Surface Mask Major Surface in 132 mm Measurement Data MeasurementData as Square Region as 148 mm Square 132 mm Square in Chuck SubstrateRegion Shape Region Flatness Simulation A convex 0.3 0.1 B convex 0.20.2 C convex 0.2 0.1 D convex 0.3 0.0 E convex 0.1 0.2 F convex 0.2 0.1G concave, NG H convex 0.2 0.2 I convex 0.3 0.4, NG J convex 0.5, NG

[0022] First, in step S101, the major surface flatness in a 148 mmsquare region of each of the quartz substrates (A to J) was measured.UltraFlat available from Tropel was used as a flatness measuringapparatus. In step S102, of the 10 quartz substrates (A to J) whichunderwent flatness measurement, nine quartz substrates (A to F, and H toJ) for which the flatness in the 148 mm square region indicated a convexshape (the mask central portion was higher than the mask peripheralportion) were selected. In addition, of the nine quartz substrates,eight quartz substrates (A to F, H, and I) for which the flatness in a132 mm square region at the central portion of the substrate majorsurface fell within the range of 0.3 μm or less were selected.

[0023] The reason why the eight quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking (vacuum chucking) in an exposure apparatus exceeds 0.3 μm, thepositional distortion of the mask pattern becomes large even though adesired flatness is obtained after chucking in the exposure apparatus.

[0024] In step S103, for each of the eight quartz substrates (A to F, Hand I), the flatness when the quartz substrate was chucked on the maskstage of an exposure apparatus was predicted by simulation using acomputer (not shown). In step S104, of the eight quartz substrates,seven quartz substrates (A to F and H) for which the flatness in the 132mm square region at the central portion of the substrate major surfaceafter chucking fell within the range of 0.3 μm or less were selected onthe basis of the prediction result.

[0025] Table 2 shows the results of flatness prediction and measurementof the seven selected quartz substrates (A to F and H) after formationof a light-shielding film. TABLE 2 Flatness of Quartz Substrate withLight-Shielding Film (μm) Consistency With Upper Upper Limit of MaskMajor Limit of Substrate Substrate Major Surface Major Surface FlatnessSurface Flatness Measurement Predicted By Simulation Predicted by Data(Measured Flatness in Simulation as as 132 mm 148 mm Square Region 148mm Square Square Region and Determination Substrate Region FlatnessFlatness Result) A 0.4 0.3 0.4 B 0.5 0.2 0.4 C 0.3 0.2 0.5, NG D 0.40.4, NG E 0.4 0.1 0.2 F 0.3 0.2 0.3 G H 0.4 0.2 0.5, NG I J

[0026] In step S105, for each of the seven quartz substrates (A to F andH), the upper limit of the flatness in the 148 mm square region of thesubstrate major surface after formation of the light-shielding film waspredicted by simulation using a computer (not shown). This upper limitrepresents a condition which ensures that when the light-shielding filmis formed on the quartz substrate, and the substrate is chucked on themask stage, the flatness in the 132 mm square region at the centralportion of the substrate major surface falls within the range of 0.3 μmor less. That is, a desired flatness of the substrate after formation ofthe light-shielding film falls within the range equal to or less thanthe upper limit.

[0027] In step S106, for each of the above-described seven quartzsubstrates (A to F and H), an HT film made of MoSiON was formed on thesubstrate major surface, and a Cr film was formed on the HT film. Instep S107, the flatness in the 148 mm square region of the major surfaceof each substrate was measured. In step S108, of the seven quartzsubstrates (A to F and H), six quartz substrates (A to C, E, F, and H)for which the flatness in the 132 mm square region at the centralportion of the substrate major surface fell within the range of 0.3 μmor less were selected on the basis of the measurement result.

[0028] In step S109, for each of the six quartz substrates (A to C, E,F, and H), the flatness measurement result after film formation wascompared with the prediction result by the simulation to determinewhether the flatness in the 148 mm square region of the substrate majorsurface was equal to or less than the above-described upper limitobtained by the simulation. In step S110, of the six quartz substrates(A to C, E, F, and H), four quartz substrates (A, B, E, and F) for whichthe flatness was equal to or less than the upper limit were selected onthe basis of the determination result. The four quartz substrates wereconsidered to be able to obtain a desired flatness after chuckingbecause the major surface flatness was equal to or less than theabove-described upper limit obtained by the simulation.

[0029] In step S111, an electron beam exposure resist was coated on thefour quartz substrates (A, B, E, and F) to prepare the quartz substratesas exposure mask substrates.

[0030] The reason why the six quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking in the exposure apparatus exceeds 0.3 μm, the positionaldistortion of the mask pattern after chucking in the exposure apparatusbecomes large even though a desired flatness is obtained after chuckingin the exposure apparatus.

[0031] Subsequently, an exposure mask manufacturing step was executed.First, four patterns having different opening ratios were drawn on theabove-described four exposure mask substrates by an electron beamlithography apparatus (EBM4000 available from NFT). Then, the substrateswere baked and developed. The Cr film and HT film were etched by areactive ion etching (RIE) apparatus (VLR-G3 available from UNAXIS). Theremaining resist was removed. The Cr film on the HT film was removed bywet etching. Four HT masks having different opening ratios were thusformed. The opening ratios of the four exposure masks were 50%, 40%,70%, and 95%.

[0032] The flatness of each exposure mask was measured while keeping itchucked on the mask stage of a wafer exposure apparatus. As a result,the flatness after chucking was 0.3 μm or less in each exposure mask,which satisfied the target value. Accordingly, a sufficient focal depthcan be obtained in photolithography in semiconductor devicemanufacturing, and the yield of semiconductor device manufacturing cangreatly be increased.

[0033] The outline of the second embodiment includes a first measurementstep of measuring the major surface flatness of a quartz substratebefore formation of a light-shielding film including a Cr film and ahalftone (HT) film, a first simulation step of simulating the majorsurface flatness when the quartz substrate is chucked on the mask stageof an exposure apparatus, a step of determining on the basis of theresult in the first simulation step whether a desired major surfaceflatness can be obtained when the quartz substrate is chucked on themask stage of the exposure apparatus, a light-shielding film formationstep of forming a light-shielding film on the quartz substrate for whichit is determined in the determination step that the desired majorsurface flatness can be obtained, a second measurement step of measuringthe major surface flatness of the substrate with the light-shieldingfilm, a second simulation step of simulating, on the basis of the resultin the second measurement step, the major surface flatness when thesubstrate with the light-shielding film is chucked on the mask stage ofthe exposure apparatus, and a determination step of determining on thebasis of the result in the second simulation step whether a desiredflatness can be obtained when the substrate with the light-shieldingfilm is chucked on the mask stage of the exposure apparatus.

[0034]FIG. 2 is a flowchart showing an exposure mask substratemanufacturing step according to the second embodiment of the presentinvention. The exposure mask substrate manufacturing step according tothe second embodiment will be described below with reference to FIG. 2and Tables 3 and 4 (described later).

[0035] Table 3 shows the results of flatness measurement and predictionof 10 quartz substrates (K to T). Each quartz substrate is 6 inchessquare (152 mm square) and has a thickness of about 6 mm. TABLE 3Flatness of Quartz Substrate (μm) Flatness in 132 mm Mask Major SurfaceMask Major Surface Square Measurement Data Measurement Data as Region as148 mm Square 132 mm Square Region in Chuck Substrate Region ShapeFlatness Simulation K convex 0.3 0.1 L convex 0.2 0.2 M concave, NG Nconvex 0.3 0.0 O convex 0.5, NG P convex 0.2 0.1 Q convex 0.2 0.4, NG Rconvex 0.2 0.2 S convex 0.3 0.4, NG T convex 0.2 0.1

[0036] First, in step S201, the major surface flatness in a 148 mmsquare region of each of the quartz substrates (K to T) was measured.UltraFlat available from Tropel was used as a flatness measuringapparatus. In step S202, of the 10 quartz substrates (K to T) whichunderwent flatness measurement, nine quartz substrates (K, L, and N toT) for which the flatness in the 148 mm square region indicated a convexshape (the mask central portion was higher than the mask peripheralportion) were selected. In addition, of the nine quartz substrates,eight quartz substrates (K, L, N, and P to T) for which the flatness ina 132 mm square region at the central portion of the substrate majorsurface fell within the range of 0.3 μm or less were selected.

[0037] The reason why the eight quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking (vacuum chucking) in an exposure apparatus exceeds 0.3 μm, thepositional distortion of the mask pattern becomes large even though adesired flatness is obtained after chucking in the exposure apparatus.

[0038] In step S203, for each of the eight quartz substrates (K, L, N,and P to T), the flatness when the quartz substrate was chucked on themask stage of an exposure apparatus was predicted by simulation using acomputer (not shown). In step S204, of the eight quartz substrates, sixquartz substrates (K, L, N, P, R, and T) for which the flatness in the132 mm square region at the central portion of the substrate majorsurface after chucking fell within the range of 0.3 μm or less wereselected on the basis of the prediction result.

[0039] Table 4 shows the results of flatness measurement and predictionof the six selected quartz substrates (K, L, N, P, R, and T) afterformation of a light-shielding film. TABLE 4 Flatness of QuartzSubstrate with Light-Shielding Film (μm) Flatness in Mask Major Surface132 mm Square Measurement Date Region in as 132 mm Square ChuckSubstrate Region Flatness Simulation K 0.2 0.3 L 0.3 0.2 M N 0.4 O P 0.30.4, NG Q R 0.2 0.5, NG S T 0.1 0.1

[0040] In step S205, for each of the above-described six quartzsubstrates (K, L, N, P, R, and T), an HT film made of MoSiON was formedon the substrate major surface, and a Cr film was formed on the HT film.In step S206, the flatness in the 148 mm square region of the majorsurface of each substrate was measured. In step S207, of the six quartzsubstrates (K, L, N, P, R, and T), five quartz substrates (K, L, P, R,and T) for which the flatness in the 132 mm square region at the centralportion of the substrate major surface fell within the range of 0.3 μmor less were selected on the basis of the measurement result.

[0041] In step S208, for each of the five quartz substrates (K, L, P, R,and T), the flatness when the quartz substrate was chucked on the maskstage of the exposure apparatus was predicted by simulation using acomputer (not shown). In step S209, of the five quartz substrates, threequartz substrates (K, L, and T) for which the flatness in the 132 mmsquare region at the central portion of the substrate major surfaceafter chucking fell within the range of 0.3 μm or less were selected onthe basis of the prediction result.

[0042] In step S210, an electron beam exposure resist was coated on thethree quartz substrates (K, L, and T) to prepare the quartz substratesas exposure mask substrates.

[0043] The reason why the five quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking in the exposure apparatus exceeds 0.3 μm, the positionaldistortion of the mask pattern after chucking in the exposure apparatusbecomes large even though a desired flatness is obtained after chuckingin the exposure apparatus.

[0044] Subsequently, an exposure mask manufacturing step was executed.First, three patterns having different opening ratios were drawn on theabove-described three exposure mask substrates by an electron beamlithography apparatus (EBM4000 available from NFT). Then, the substrateswere baked and developed. The Cr film and HT film were etched by areactive ion etching (RIE) apparatus (VLR-G3 available from UNAXIS). Theremaining resist was removed. The Cr film on the HT film was removed bywet etching. Three HT masks having different opening ratios were thusformed. The opening ratios of the three exposure masks were 50%, 50%,and 95%.

[0045] The flatness of each exposure mask was measured while keeping itchucked on the mask stage of a wafer exposure apparatus. As a result,the flatness after chucking was 0.3 μm or less in each exposure mask,which satisfied the target value. Accordingly, a sufficient focal depthcan be obtained in photolithography in semiconductor devicemanufacturing, and the yield of semiconductor device manufacturing cangreatly be increased.

[0046] The outline of the third embodiment includes a first measurementstep of measuring the major surface flatness of a quartz substratebefore formation of a light-shielding film including a Cr film and ahalftone (HT) film, a step of simulating the major surface flatnessafter formation of the light-shielding film, which makes it possible toobtain a desired major surface flatness when a substrate prepared byforming the light-shielding film on the quartz substrate at a desiredcoverage is chucked on the mask stage of an exposure apparatus, a secondmeasurement step of measuring the major surface flatness of thesubstrate after the light-shielding film is actually formed on thequartz substrate, and a step of comparing the result in the secondmeasurement step with the simulation result to determine whether thedesired flatness can be obtained.

[0047]FIG. 3 is a flowchart showing an exposure mask substratemanufacturing step according to the third embodiment of the presentinvention. The exposure mask substrate manufacturing step according tothe third embodiment will be described below with reference to FIG. 3and Tables 5 and 6 (described later).

[0048] Table 5 shows the results of flatness measurement and predictionof 10 quartz substrates (A to J). Each quartz substrate is 6 inchessquare (152 mm square) and has a thickness of about 6 mm. TABLE 5Flatness of Quartz Substrate (μm) Mask Major Mask Major Surface SurfaceMeasurement Data Measurement Data as 148 mm Square as 132 mm SquareSubstrate Region Shape Region Flatness A convex 0.3 B convex 0.2 Cconvex 0.2 D convex 0.3 E convex 0.1 F convex 0.2 G convex 0.3 H convex0.2 I convex 0.3 J convex 0.5, NG

[0049] First, in step S301, the major surface flatness in a 148 mmsquare region of each of the quartz substrates (A to J) was measured.UltraFlat available from Tropel was used as a flatness measuringapparatus. In step S302, of the 10 quartz substrates (A to J) whichunderwent flatness measurement, 10 quartz substrates (A to J) for whichthe flatness in the 148 mm square region indicated a convex shape (themask central portion was higher than the mask peripheral portion) wereselected. In addition, of the 10 quartz substrates, nine quartzsubstrates (A to I) for which the flatness in a 132 mm square region atthe central portion of the substrate major surface fell within the rangeof 0.3 μm or less were selected.

[0050] The reason why the nine quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking (vacuum chucking) in an exposure apparatus exceeds 0.3 μm, thepositional distortion of the mask pattern becomes large even though thedesired flatness is obtained after chucking in the exposure apparatus.

[0051] Table 6 shows the results of flatness prediction and measurementof the nine selected quartz substrates (A to I) after formation of alight-shielding film. TABLE 6 Flatness of Quartz Substrate withLight-Shielding Film (μm) Range of Substrate Major Surface FlatnessPredicted by Mask Major Consistency Simulation Surface with Substrate(Coverage: 50 to Measurement Data Major Surface 100%) in 148 mm as 148mm Square Flatness Predicted Substrate Square Region Region Flatness bySimulation A 0.2-0.4 0.3 OK B 0.1-0.3 0.2 OK C 0.1-0.3 0.2 OK D 0.2-0.40.5 NG E   0-0.2 0.1 OK F 0.1-0.3 0.2 OK G 0.2-0.4 0.4 OK H 0.1-0.3 0.2OK I 0.2-0.4 −0.1 NG J

[0052] In step S303, for each of the nine quartz substrates (A to I),the range of the flatness in the 148 mm square region of the substratemajor surface after the light-shielding film was formed on the substratemajor surface was predicted by simulation using a computer (not shown).This range represents a condition which ensures that when thelight-shielding film is formed on the quartz substrate at a coverage of50 to 100%, and the substrate is chucked on the mask stage, the flatnessin the 132 mm square region at the central portion of the substratemajor surface falls within the range of 0.3 μm or less. That is, adesired flatness of the substrate after formation of the light-shieldingfilm falls within the range.

[0053] In step S304, for each of the above-described nine quartzsubstrates (A to I), an HT film made of MoSiON was formed on thesubstrate major surface, and a Cr film was formed on the HT film. Instep S305, the flatness in the 148 mm square region of the major surfaceof each substrate was measured. In step S306, of the nine quartzsubstrates (A to I), nine quartz substrates (A to I) for which theflatness in the 132 mm square region at the central portion of thesubstrate major surface fell within the range of 0.3 μm or less wereselected on the basis of the measurement result.

[0054] In step S307, for each of the nine quartz substrates (A to I),the flatness measurement result after film formation was compared withthe prediction result by the simulation to determine whether theflatness in the 148 mm square region of the substrate major surface fellwithin the range obtained by the simulation. In step S308, of the ninequartz substrates (A to I), seven quartz substrates (A to C, and E to H)for which the flatness fell within the range were selected on the basisof the determination result. The seven quartz substrates were consideredto be able to obtain a desired flatness after chucking because the majorsurface flatness fell within the above-described range obtained by thesimulation.

[0055] In step S309, an electron beam exposure resist was coated on theseven quartz substrates (A to C, and E to H) to prepare the quartzsubstrates as exposure mask substrates.

[0056] The reason why the nine quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking in the exposure apparatus exceeds 0.3 μm, the positionaldistortion of the mask pattern after chucking in the exposure apparatusbecomes large even though a desired flatness is obtained after chuckingin the exposure apparatus.

[0057] Subsequently, an exposure mask manufacturing step was executed.First, three patterns having different opening ratios were drawn onthree of the above-described seven exposure mask substrates by anelectron beam lithography apparatus (EBM4000 available from NFT). Then,the substrates were baked and developed. The Cr film and HT film wereetched by a reactive ion etching (RIE) apparatus (VLR-G3 available fromUNAXIS). The remaining resist was removed. The Cr film on the HT filmwas removed by wet etching. Three HT masks having different openingratios were thus formed. The opening ratios of the three exposure maskswere 50%, 70%, and 95%.

[0058] The flatness of each exposure mask was measured while keeping itchucked on the mask stage of a wafer exposure apparatus. As a result,the flatness after chucking was 0.3 μm or less in each exposure mask,which satisfied the target value. Accordingly, a sufficient focal depthcan be obtained in photolithography in semiconductor devicemanufacturing, and the yield of semiconductor device manufacturing cangreatly be increased.

[0059] In the third embodiment, a desired light-shielding film coverageis 50 to 100%. If the light-shielding film coverage is 0 to 50%, i.e.,includes 0%, the flatness of each quartz substrate chucked on the maskstage of the wafer exposure apparatus may be predicted first bysimulation using the computer (not shown) on the basis of the flatnessmeasurement result for the quartz substrate before formation of thelight-shielding film. After chucking, quartz substrates for which theflatness in the 132 mm square region at the central portion of thesubstrate major surface equals the desired flatness are selected. Then,a light-shielding film may be formed on each quartz substrate.

[0060] The outline of the fourth embodiment includes a first measurementstep of measuring the major surface flatness of a quartz substratebefore formation of a light-shielding film including a Cr film and ahalftone (HT) film, a first simulation step of simulating the majorsurface flatness when the quartz substrate is chucked on the mask stageof an exposure apparatus, a step of determining on the basis of theresult in the first simulation step whether a desired major surfaceflatness can be obtained when the quartz substrate is chucked on themask stage of the exposure apparatus, a light-shielding film formationstep of forming a light-shielding film on the quartz substrate for whichit is determined in the determination step that the desired majorsurface flatness can be obtained, a second measurement step of measuringthe major surface flatness of the substrate with the light-shieldingfilm, a second simulation step of simulating, on the basis of the resultin the second measurement step, the major surface flatness when thesubstrate with the light-shielding film at a desired light-shieldingfilm coverage is chucked on the mask stage of the exposure apparatus,and a determination step of determining on the basis of the result inthe second simulation step whether the desired flatness can be obtainedwhen the quartz substrate with the light-shielding film is chucked onthe mask stage of the exposure apparatus.

[0061]FIG. 4 is a flowchart showing an exposure mask substratemanufacturing step according to the fourth embodiment of the presentinvention. The exposure mask substrate manufacturing step according tothe fourth embodiment will be described below with reference to FIG. 4and Tables 7 and 8 (described later).

[0062] Table 7 shows the results of flatness measurement and predictionof 10 quartz substrates (K to T). Each quartz substrate is 6 inchessquare (152 mm square) and has a thickness of about 6 mm. TABLE 7Flatness of Quartz Substrate (μm) Flatness Mask Major Surface Mask MajorSurface in 132 mm Measurement Data Measurement Data as Square Region as148 mm Square 132 mm Square in Chuck Substrate Region Shape RegionFlatness Simulation K convex 0.3 0.1 L convex 0.2 0.2 M concave, NG Nconvex 0.3 0.0 O convex 0.5, NG P convex 0.2 0.1 Q convex 0.2 0.4, NG Rconvex 0.2 0.2 S convex 0.3 0.4, NG T convex 0.2 0.1

[0063] First, in step S401, the major surface flatness in a 148 mmsquare region of each of the quartz substrates (K to T) was measured.UltraFlat available from Tropel was used as a flatness measuringapparatus. In step S402, of the 10 quartz substrates (K to T) whichunderwent flatness measurement, nine quartz substrates (K, L, and N toT) for which the flatness in the 148 mm square region indicated a convexshape (the mask central portion was higher than the mask peripheralportion) were selected. In addition, of the nine quartz substrates,eight quartz substrates (K, L, N, and P to T) for which the flatness ina 132 mm square region at the central portion of the substrate majorsurface fell within the range of 0.3 μm or less were selected.

[0064] The reason why the eight quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking (vacuum chucking) in an exposure apparatus exceeds 0.3 μm, thepositional distortion of the mask pattern becomes large even though thedesired flatness is obtained after chucking in the exposure apparatus.

[0065] In step S403, for each of the eight quartz substrates (K, L, N,and P to T), the flatness when the quartz substrate was chucked on themask stage of an exposure apparatus was predicted by simulation using acomputer (not shown). In step S404, of the eight quartz substrates, sixquartz substrates (K, L, N, P, R, and T) for which the flatness in the132 mm square region at the central portion of the substrate majorsurface after chucking fell within the range of 0.3 μm or less wereselected on the basis of the prediction result.

[0066] Table 8 shows the results of flatness measurement and predictionof the six selected quartz substrates (K, L, N, P, R, and T) afterformation of a light-shielding film. TABLE 8 Flatness of QuartzSubstrate with Light-Shielding Film (μm) Flatness in Chuck Mask MajorSimulation Surface (Light-Shielding Measurement Data Film Coverage 0 as132 mm Square to 50%) in 132 mm Substrate Region Flatness Square RegionK 0.2 0.2-0.3 L 0.3 0.2-0.3 M N 0.4 O P 0.3 0.2-0.3 Q R 0.2 0.2 S T 0.10.1-0.2

[0067] In step S405, for each of the above-described six quartzsubstrates (K, L, N, P, R, and T), an HT film made of MoSiON was formedon the substrate major surface, and a Cr film was formed on the HT film.In step S406, the flatness in the 148 mm square region of the majorsurface of each substrate was measured. In step S407, of the six quartzsubstrates (K, L, N, P, R, and T), five quartz substrates (K, L, P, R,and T) for which the flatness in the 132 mm square region at the centralportion of the substrate major surface fell within the range of 0.3 μmor less were selected on the basis of the measurement result.

[0068] In step S408, for each of the five quartz substrates (K, L, P, R,and T), the flatness when the light-shielding film coverage was 0 to50%, and the quartz substrate was chucked on the mask stage of theexposure apparatus was predicted by simulation using a computer (notshown). In step S409, of the five quartz substrates, five quartzsubstrates (K, L, P, R, and T) for which the flatness in the 132 mmsquare region at the central portion of the substrate major surfaceafter chucking fell within the range of 0.3 μm or less were selected onthe basis of the prediction result.

[0069] In step S410, an electron beam exposure resist was coated on thefive quartz substrates (K, L, P, R, and T) to prepare the quartzsubstrates as exposure mask substrates.

[0070] The reason why the five quartz substrates for which the flatnessin the 132 mm square region at the central portion of the substratemajor surface fell within the range of 0.3 μm or less were selectedfirst is as follows. In a quartz substrate whose flatness beforechucking in the exposure apparatus exceeds 0.3 μm, the positionaldistortion of the mask pattern after chucking in the exposure apparatusbecomes large even though the desired flatness is obtained afterchucking in the exposure apparatus.

[0071] Subsequently, an exposure mask manufacturing step was executed.First, three patterns having different opening ratios were drawn onthree of the above-described five exposure mask substrates by anelectron beam lithography apparatus (EBM4000 available from NFT). Then,the substrates were baked and developed. The Cr film and HT film wereetched by a reactive ion etching (RIE) apparatus (VLR-G3 available fromUNAXIS). The remaining resist was removed. The Cr film on the HT filmwas removed by wet etching. Three HT masks having different openingratios were thus formed. The opening ratios of the three exposure maskswere 5%, 30%, and 50%.

[0072] The flatness of each exposure mask was measured while keeping itchucked on the mask stage of a wafer exposure apparatus. As a result,the flatness after chucking was 0.3 μm or less in each exposure mask,which satisfied the target value. Accordingly, a sufficient focal depthcan be obtained in photolithography in semiconductor devicemanufacturing, and the yield of semiconductor device manufacturing cangreatly be increased.

[0073] An exposure mask manufactured by using an exposure mask substratemanufactured by the exposure mask substrate manufacturing step describedin each of the above embodiments is chucked in an exposure apparatus. Apattern formed on the exposure mask, which is to be used to form asemiconductor element, is illuminated by an illumination optical systemto transfer the image of the pattern onto a predetermined substrate.With this processing, a semiconductor device can be manufactured.

[0074] As described above, according to the embodiments, flatnesssimulation after chucking is done on the basis of the substrate flatnessmeasurement data before formation of a light-shielding film, andsubstrates having a desired flatness are selected. Next, the flatnessafter light-shielding film formation, which should ensure a desiredflatness when a light-shielding film is formed on the substrate, isestimated. After a light-shielding film is actually formed on eachsubstrate, it is determined whether the substrate satisfies theestimated flatness. Substrates that satisfy the flatness are used asexposure mask substrates. When a wafer is exposed by using an exposuremask manufactured by the above method, the focal tolerance can greatlyand reliably be made larger than before.

[0075] The present invention is not limited to the above embodiments,and various changes and modifications can appropriately be made withinthe spirit and scope of the present invention. For example, thelight-shielding film need not be limited to MoSiON or Cr. A Ta compoundor a silicon nitride compound may also be used. The substrate need notbe limited to a quartz substrate, either. A silicon substrate or anelectron beam exposure mask substrate may be used. In step S105 or S303,simulation can be executed to obtain a desired flatness assuming notonly that the substrate is chucked on one kind of mask stage but alsothat the substrate is chucked on two or more kinds of mask stage.

[0076] According to one aspect of the present invention, an exposuremask substrate manufacturing method capable of manufacturing an exposuremask substrate having a desired flatness can be provided.

[0077] According to another aspect of the present invention, an exposuremask manufacturing method capable of manufacturing an exposure maskusing an exposure mask substrate having a desired flatness can beprovided.

[0078] According to still another aspect of the present invention, asemiconductor device manufacturing method capable of manufacturing asemiconductor device by using an exposure mask using an exposure masksubstrate having a desired flatness can be provided.

[0079] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A method of manufacturing an exposure masksubstrate including a substrate and a light-shielding film formed on thesubstrate, comprising: measuring a flatness of at least one substratebefore formation of a light-shielding film; predicting, on the basis ofa measurement result, the flatness of the substrate when the substrateis chucked on an exposure apparatus; selecting the substrate having apredetermined flatness on the basis of a prediction result; predicting,for the selected substrate, a desired flatness of the substrate afterlight-shielding film formation after a light-shielding film is formed onthe substrate; forming a light-shielding film on the selected substrate;measuring the flatness of the substrate having the formedlight-shielding film; and determining whether the substrate having thelight-shielding film has the desired flatness after light-shielding filmformation by comparing a measurement result with a prediction result ofthe flatness after light-shielding film formation.
 2. The methodaccording to claim 1, wherein in predicting the flatness afterlight-shielding film formation, the desired flatness of the substrateafter light-shielding film formation after the light-shielding film isformed at a predetermined coverage is predicted.
 3. The method accordingto claim 1, wherein the desired flatness after light-shielding filmformation is a flatness of the substrate after light-shielding filmformation, which ensures that when the substrate is chucked on theexposure apparatus, a flatness in a region of a central portion of amajor surface of the substrate has not more than a predetermined value.4. The method according to claim 2, wherein the desired flatness afterlight-shielding film formation is a flatness of the substrate afterlight-shielding film formation, which ensures that when the substrate ischucked on the exposure apparatus, a flatness in a region of a centralportion of a major surface of the substrate has not more than apredetermined value.
 5. A method of manufacturing an exposure masksubstrate including a substrate and a light-shielding film formed on thesubstrate, comprising: measuring a flatness of at least one substratebefore formation of a light-shielding film; predicting, on the basis ofa measurement result, the flatness of the substrate when the substrateis chucked on an exposure apparatus; selecting the substrate having apredetermined first flatness on the basis of a prediction result;forming a light-shielding film on the selected substrate; measuring theflatness of the substrate after light-shielding film formation, thesubstrate having the formed light-shielding film; predicting, on thebasis of a measurement result, the flatness of the substrate when thesubstrate after formation of the light-shielding film is chucked on theexposure apparatus; and selecting the substrate having a predeterminedsecond flatness on the basis of a prediction result.
 6. The methodaccording to claim 5, wherein in predicting the flatness afterlight-shielding film formation, the flatness of the substrate after thelight-shielding film is formed at a predetermined coverage is predicted.7. An exposure mask manufacturing method of manufacturing an exposuremask by using an exposure mask substrate including a substrate and alight-shielding film formed on the substrate, comprising: measuring aflatness of at least one substrate before formation of a light-shieldingfilm; predicting, on the basis of a measurement result, the flatness ofthe substrate when the substrate is chucked on an exposure apparatus;selecting the substrate having a predetermined flatness on the basis ofa prediction result; predicting, for the selected substrate, a desiredflatness of the substrate after light-shielding film formation after alight-shielding film is formed on the substrate; forming alight-shielding film on the selected substrate; measuring the flatnessof the substrate having the formed light-shielding film; andmanufacturing an exposure mask by forming a desired pattern on thesubstrate when it is determined by comparing a measurement result with aprediction result of the flatness after light-shielding film formationthat the substrate having the light-shielding film has the desiredflatness after light-shielding film formation.
 8. The method accordingto claim 7, wherein in predicting the flatness after light-shieldingfilm formation, the desired flatness of the substrate afterlight-shielding film formation after the light-shielding film is formedat a predetermined coverage is predicted.
 9. The method according toclaim 7, wherein the desired flatness after light-shielding filmformation is a flatness of the substrate after light-shielding filmformation, which ensures that when the substrate is chucked on theexposure apparatus, a flatness in a region of a central portion of amajor surface of the substrate has not more than a predetermined value.10. The method according to claim 8, wherein the desired flatness afterlight-shielding film formation is a flatness of the substrate afterlight-shielding film formation, which ensures that when the substrate ischucked on the exposure apparatus, a flatness in a region of a centralportion of a major surface of the substrate has not more than apredetermined value.
 11. An exposure mask manufacturing method ofmanufacturing an exposure mask by using an exposure mask substrateincluding a substrate and a light-shielding film formed on thesubstrate, comprising: measuring a flatness of at least one substratebefore formation of a light-shielding film; predicting, on the basis ofa measurement result, the flatness of the substrate when the substrateis chucked on an exposure apparatus; selecting the substrate having apredetermined first flatness on the basis of a prediction result;forming a light-shielding film on the selected substrate; measuring theflatness of the substrate after light-shielding film formation, thesubstrate having the formed light-shielding film; predicting, on thebasis of a measurement result, the flatness of the substrate when thesubstrate after formation of the light-shielding film is chucked on theexposure apparatus; selecting the substrate having a predeterminedsecond flatness on the basis of a prediction result; and manufacturingan exposure mask by forming a desired pattern on the selected substrate.12. The method according to claim 11, wherein in predicting the flatnessafter light-shielding film formation, the flatness of the substrateafter the light-shielding film is formed at a predetermined coverage ispredicted.
 13. A semiconductor device manufacturing method comprising:chucking an exposure mask manufactured by an exposure mask manufacturingmethod of claim 7 in an exposure apparatus; and illuminating a patternformed on the exposure mask, which is to be used to form a semiconductorelement, by an illumination optical system to transfer an image of thepattern onto a predetermined substrate.
 14. A semiconductor devicemanufacturing method comprising: chucking an exposure mask manufacturedby an exposure mask manufacturing method of claim 8 in an exposureapparatus; and illuminating a pattern formed on the exposure mask, whichis to be used to form a semiconductor element, by an illuminationoptical system to transfer an image of the pattern onto a predeterminedsubstrate.
 15. A semiconductor device manufacturing method comprising:chucking an exposure mask manufactured by an exposure mask manufacturingmethod of claim 9 in an exposure apparatus; and illuminating a patternformed on the exposure mask, which is to be used to form a semiconductorelement, by an illumination optical system to transfer an image of thepattern onto a predetermined substrate.
 16. A semiconductor devicemanufacturing method comprising: chucking an exposure mask manufacturedby an exposure mask manufacturing method of claim 10 in an exposureapparatus; and illuminating a pattern formed on the exposure mask, whichis to be used to form a semiconductor element, by an illuminationoptical system to transfer an image of the pattern onto a predeterminedsubstrate.
 17. A semiconductor device manufacturing method comprising:chucking an exposure mask manufactured by an exposure mask manufacturingmethod of claim 11 in an exposure apparatus; and illuminating a patternformed on the exposure mask, which is to be used to form a semiconductorelement, by an illumination optical system to transfer an image of thepattern onto a predetermined substrate.
 18. A semiconductor devicemanufacturing method comprising: chucking an exposure mask manufacturedby an exposure mask manufacturing method of claim 12 in an exposureapparatus; and illuminating a pattern formed on the exposure mask, whichis to be used to form a semiconductor element, by an illuminationoptical system to transfer an image of the pattern onto a predeterminedsubstrate.